Gas turbines, such as aircraft engines, include as a rule multiple stages with rotating blades and stationary guide blades, the rotating blades rotating together with a rotor and the rotating blades as well as the guide blades being enclosed by a stationary housing of the gas turbine. For enhancing the power of an aircraft engine it is important to optimize all components and subsystems. This includes the sealing systems in aircraft engines. It is particularly problematic in aircraft engines to maintain a minimum gap between the rotating blades and the stationary housing of a high-pressure compressor. The highest temperatures as well as the greatest temperature gradients occur in high-pressure compressors, which makes it complicated to maintain the gap between the rotating blades and the stationary housing of the compressor. This, among other things, is the reason for dispensing with shroud bands on compressor rotating blades, such as are used in turbines.
As mentioned above, rotating blades in the compressor do not have a shroud band. Therefore, the ends or tips of the rotating blades are exposed to a direct frictional contact with the housing during the rubbing into the stationary housing. Such a rubbing of the tips of the rotating blades into the housing is caused by manufacturing tolerances during adjustment of a minimum radial gap. Since material is removed from the rotating blades due to the frictional contact of the tips of the rotating blades, an undesirable enlargement of the gap may occur over the entire circumference of the housing and the rotor. In order to prevent this, it is known from the related art to armor the ends or tips of the rotating blades using a hard coating or abrasive particles. However, such blade tip armoring is very expensive.
Another way to avoid the wear at the tips of the rotating blades and to provide an optimized seal between the ends or tips of the rotating blades and the stationary housing is coating the housing with a running-in coating. When material is removed on a running-in coating, the radial gap is not enlarged over the entire circumference, but as a rule only in a sickle shape in one or in multiple sectors, thereby reducing a power drop of the engine. Housings having a running-in coating are known from the related art.
A running-in coating for the housing of a high-pressure compressor is known from the related art, the running-in coating being made of a NiCrAl-bentonite material. Such a running-in coating made of a nickel-chromium-aluminum-bentonite material is particularly well suited for rotating blades which are made of a nickel material or a nickel-based alloy. However, it has become apparent that such a running-in coating is not suitable for blades made of a titanium material or a titanium-based alloy. Unarmored blade tips of blades made of a titanium-based material are damaged when a NiCrAl-bentonite material is used. Therefore, according to the related art, the blade tips of rotating blades made of a titanium-based material must be armored for temperatures higher than 480° C. when such a running-in coating is used. There is no running-in coating known from the related art with the aid of which armoring of the blade tips may be dispensed with, both in the case of rotating blades made of a nickel-based material and of rotating blades made of a titanium-based material.